Vinnichenko M.V., Pham M.T., Chevolleau T., Poperenko L.V., Maitz M.F. In situ ellipsometric investigation of stainless steel corrosion behavior in biological media. Appl Surf Sci 207(1-4): 176-182 (2003).
The corrosion of metals is associated both with a release of ions and changes in optical surface properties. In this study these two effects were
correlated by a potentiodynamic corrosion test and in situ probing of the surface by ellipsometry. The studies were carried out with stainless steel AISI 304 and 316 in phosphate buffered saline (PBS) and in Dulbecco's Modified Minimal Essential Medium (DMEM) at pH 7.4. In both media 304 steel is more susceptible to corrosion than 316 grade. The 316 steel shows higher corrosion potential and higher corrosion current density in PBS than in DMEM, for 304 steel this behavior is vice versa.
Ellipsometry demonstrated a higher sensitivity than potentiodynamics to surface modification in the cathodic area. In DMEM the removal of a surface layer at negative voltage and a further repassivation with increasing voltage was characteristic. In PBS a surface layer started to grow immediately. X-ray photoelectron spectra of this layer formed in PBS are consistent with iron phosphate. Its formation is inhibited in DMEM; the presence of aminoacids is discussed as the reason.